//
// async_tcp_echo_server.cpp
// ~~~~~~~~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
//
// Distributed under the Boost Software License, Version 1.0.
// (See http://www.boost.org/LICENSE_1_0.txt)
//

#include <cstdlib>
#include <iostream>
#include <memory>
#include <utility>

#include "asio.hpp"

// An asynchronous tcp echo server.
// See https://think-async.com/Asio/asio-1.16.1/src/examples/cpp11/echo/async_tcp_echo_server.cpp

using asio::ip::tcp;

class session : public std::enable_shared_from_this<session> {
public:
  session(tcp::socket socket) : socket_(std::move(socket)) {}

  void start() { do_read(); }

private:
  void do_read() {
    auto self(shared_from_this());
    socket_.async_read_some(asio::buffer(data_, max_length),
                            [this, self](std::error_code ec, std::size_t length) {
                              if (!ec) {
                                do_write(length);
                              }
                            });
  }

  void do_write(std::size_t length) {
    auto self(shared_from_this());
    asio::async_write(socket_, asio::buffer(data_, length),
                      [this, self](std::error_code ec, std::size_t /*length*/) {
                        if (!ec) {
                          do_read();
                        }
                      });
  }

  tcp::socket socket_;
  enum { max_length = 1024 };
  char data_[max_length];
};

class server {
public:
  server(asio::io_context& io_context, short port)
      : acceptor_(io_context, tcp::endpoint(tcp::v4(), port)) {
    do_accept();
  }

private:
  void do_accept() {
    acceptor_.async_accept([this](std::error_code ec, tcp::socket socket) {
      if (!ec) {
        std::make_shared<session>(std::move(socket))->start();
      }

      do_accept();
    });
  }

  tcp::acceptor acceptor_;
};

int main(int argc, char* argv[]) {
  try {
    if (argc != 2) {
      std::cerr << "Usage: async_tcp_echo_server <port>\n";
      return 1;
    }

    asio::io_context io_context;

    server s(io_context, std::atoi(argv[1]));

    io_context.run();
  } catch (std::exception& e) {
    std::cerr << "Exception: " << e.what() << "\n";
  }

  return 0;
}
